Porous ceramic foam materials are known in the art, for example, having been described in U.S. Pat. Nos. 3,090,094 and 3,097,930. These porous ceramic foam materials are known to be particularly useful in filtering molten metal, as described in the aforesaid copending application U.S. Ser. No. 430,229, now U.S. Pat. No. 3,893,917 for "Improved Molten Metal Filter" by Michael J. Pryor and Thomas J. Gray.
Molten metal, particularly molten aluminum, in practice generally contains entrained solids which are deleterious to the final cast metal product. These entrained solids appear as inclusions in the final cast product after the molten metal is solidified and cause the final product to be less ductile or to have poor bright finishing and anodizing characteristics. The inclusions may originate from several sources. For example, the inclusions may originate from surface oxide films which become broken up and are entrained in the resultant molten metal. In addition, the inclusions may originate as insoluble impurities, such as carbides, borides and others or eroded furnace and trough refractories.
It is naturally highly desirable to devise an improved filter for use in removing or minimizing entrained solids from the final cast product, particularly with respect to molten aluminum and especially when the resultant metal is to be used in a decorative product, such as decorative trim or sheet made from aluminum Alloy 5252.
Ceramic foam materials are known to be highly useful in filtering molten metal, particularly molten aluminum, as disclosed in the aforesaid copending application U.S. Ser. No. 430,229. It is highly desirable and it is a principal object of the present invention to devise a ceramic foam filter which has considerable high temperature resistance so that it can be used on a variety of molten metals and so that the structure thereof is resistant to degradation under the severe conditions of use associated with filtration of molten metal.
It is a further object of the present invention to devise a high temperature resistant ceramic foam filter as aforesaid which is convenient to prepare and is characterized by reasonable cost.
It is a still further object of the present invention to provide a high temperature resistant foam filter as aforesaid which does not contaminate the melt and does not result in degradation of desirable characteristics in the final metal product.
Further objects and advantages of the present invention will appear hereinafter.